In the U.S., more than 45,000 women are diagnosed with cancer during adolescence and young adulthood (AYA, ages 15-39 at diagnosis) each year. Fertility and reproductive outcomes are critical issues for AYA cancer survivors but little is known about the effect of diagnosis and treatment on the clinical course and outcome of future pregnancy. Our study will leverage existing data sources to assess clinical pregnancy outcomes among women with the most common AYA cancers (lymphoma, breast, melanoma, thyroid and gynecologic cancer) that account for >70% of all diagnoses. Our findings will provide urgently needed answers that can be directly applied to fertility preservation, preconception, and prenatal counseling. Data for this study come from the Kaiser Permanente (KP) Northern and Southern California integrated healthcare systems and from an innovative linkage of the North Carolina Central Cancer Registry, public and private administrative cancer treatment claims, and North Carolina birth certificates. We will also use information from the nation-wide Society for Assisted Reproductive Technology Clinic Outcome Reporting System to identify fertility and assisted reproductive procedures among all women (with a cancer diagnosis or without) in our study. This research has 3 aims?we will: (1.) Assess pregnancy risks among >7,000 female AYA cancer survivors enrolled in the KP California health care systems using a validated algorithm to identify pregnancies and outcomes (miscarriage, termination, livebirth) in the electronic medical record. Next we will: (2.) Assess risk of adverse infant birth outcomes (low birth weight, small for gestational age, preterm birth) among 2,700 births to 13,500 AYA cancer survivors enrolled in the KP California health care systems or living in North Carolina. The final aim is to: (3.) Examine factors that may contribute to risk of pregnancy loss or adverse birth outcomes including cancer type, age at diagnosis, time since diagnosis, cancer treatment, minority or low income status, and use of fertility preservation or assisted reproductive technologies. Pregnancy and birth risks among AYA cancer survivors will be compared to women without a prior cancer diagnosis at each site and also among survivors to compare specific treatment or diagnosis characteristics. This research uses multiple, existing data sources that include detailed information on cancer treatment and fertility procedures in the U.S. during recent years (2000-2016). Our population-level study will inform survivorship planning as fertility and parenthood are addressed more widely across the cancer care continuum. In the future, the AYA cancer survivor population identified as part of this proposal can be followed to assess cancer recurrence risk, non-reproductive organ system effects of cancer treatment or pregnancy, and developmental outcomes in offspring. Results from this study will provide an important evidence base for counseling women who must make difficult decisions about future childbearing intentions while simultaneously confronting a cancer diagnosis.